Thursday, May 08, 2008

Pluck from the sky



When talking about engineering, we deal with numbers. Most of the time, beside formula, we use also constants and factors. For non-technical person, they are wonder where we get the figure, but for us, we know we didn’t pluck it from the sky.

Where we get those figures?

There are many ways. First, from books, research papers, published technical information. Normally we call these kinds of numbers as constant. Like speed of light, c, is equal to 299792458 m/s. How to get this figure is a long story and if you interested, you may read the following wiki.

The other way of getting the number is from experience, rule-of-thumb and common practice. For example, we use 1 pa/m friction loss when sizing the air-cond duct. Why? Well, it just a factor that everyone is practice when sizing the duct. For different application, we use different factor in sizing. There is a math and theory behind it but we are just engineer not scientist, therefore, using a practiced figure shall not be harmful, unless you choice it wrongly.

And the final way to get the number is by trial-and-error. Well, this is a hard way, but when both the two mentioned methods to get factor/constant are not available, we need to do some guessing or a better word is reverse engineering. This is commonly use when study people’s design and when not much of detail information left by the designer. In this case, guessing and reverse engineering is the only way to know the mind of a designer. It needs a wise guy to guess the mind of a genius /wahaha. If you knowledgeable enough, most of the time, you can hit very near to the target.

So, after this, if you saw some numbers pop up from the words, please don’t say we are pluck from the sky, it is not so easy to get all these numbers and we also don’t have time to tell or explain to you how to get these since you may not from engineering stream. And actually, there is nothing left on the sky already /XD